Converters, used in particular for preparing and refining steel by blowing air or oxygen into a molten metal bath, generally consist of an elongated vessel into which a liquid-metal bath to be treated, for example pig iron, is charged.
The vessel consists of a side wall, generally generated by revolution about an axis and defining a treatment space closed at one end by a bottom and opening out at its other end into a charging and casting orifice, the side wall and the bottom being covered by a refractory lining.
It is known that the vessel must be located in a vertical position for blowing of air or oxygen, and then tilted through rotation about a horizontal axis so that the metal can be cast after treatment. For this purpose, the vessel is located between two raised fixed supports on which it rests by means of two rotational-bearing members which are diametrically opposite to each other and centered on the same horizontal axis about which the vessel is able to pivot through the action of an operating means.
This type of apparatus, which has been known since the beginning of the metallurgical industry, has obviously been the subject of numerous improvements associated with progress in the art, and the method of supporting the vessel with respect to the rotating support members which define the tilting axis is particularly important because the behavior of the vessel and the support members and their performance over time depend on it, even more so since the mass of liquid metal treated during an operation and, consequently, the dimensions and the weight of the converter have become very important.
Generally speaking, the support members are subject, on the one hand, to the mechanical loads which depend on the intrinsic weight of the vessel and the refractory materials, the charge of molten metal and/or of scrap and the vibrations caused by treatment and, on the other hand, to the thermal stresses due to the temperature of the molten-metal charge inside the vessel, to the heat released by the blowing of air or oxygen during processing and to the radiation during deslagging or steel pouring.
To date, it has seemed obvious to construct, in the form of clearly separate members, on the one hand, the treatment vessel covered internally with a refractory lining so as to withstand the high temperatures due to treatment and, on the other hand, its support members which comprise, generally, a circular ring defining an orifice inside which the vessel may be inserted, bearing on the two fixed supports, by means of trunnions.
The tilting movement is applied onto the ring which rotates about its trunnions, causing the vessel to move as well. For this purpose, the tilting torque may advantageously be applied onto a rim with a fairly large diameter, which is keyed onto one of the trunnions and rotation of which is controlled by a speed-reducing unit (see FR-A-1,550,338). Such a rim, in the form of a cylindrical collar centered on the tilting axis, may also be mounted rotatably on rollers so as to serve as a bearing member for the ring (see FR-A-1,257,664).
The treatment, support and tilting functions are thus ensured by separate members, which consequently may be provided. For example, the ring may be cooled by circulating water, this not being possible in the case of the vessel. Moreover, so as to allow relative movements and expansion, the vessel is generally supported by the ring only at particular support points.
Such an embodiment is, however, very heavy and expensive since the ring must support not only the weight of the vessel, but also the torques due to pivoting. The actual weight of the ring may, moreover, be of the same order as that of the vessel.
Furthermore, the forces involved in supporting the vessel on the ring are delicately distributed in a manner which is rarely isostatic, so much so that differential stresses appear, the load distribution is disturbed and the stresses are unbalanced.
Generally, however, such an embodiment has apparently proved to be satisfactory and has therefore been widely used, it being possible to overcome its drawbacks by use of various mechanical or thermal devices. However, all these arrangements complicate installation, operation and maintenance thereof, increasing the cost without, however, eliminating all the problems.